二叉排序树插入问题求助

#include<cstdio>
#include<iostream>
int n,a;
struct Node{
	int data;
	Node *lson,*rson;
}*root;
void Insert(int num,Node *p)
{
	if(p==NULL)
	{
		p=new Node;
		p->data=num;
	}
	else
		num<p->data?Insert(num,p->lson):Insert(num,p->rson);
}
void dfs(Node *p)
{
	if(p!=NULL)
	{
		dfs(p->lson);
		printf("%d\n",p->data);
		dfs(p->rson);
	}
}
int main(int argc, char const *argv[])
{
	freopen("test.txt","r",stdin);
	scanf("%d",&n);
	for(int i=1;i<=n;++i)
		scanf("%d",&a),Insert(a,root);
	dfs(root);
	return 0;
}